Peroxomonosulphuric acid is a strong oxidant which reacts faster than hydrogen peroxide and can be readily made from concentrated sulphuric acid and aqueous hydrogen peroxide, as known from U.S. Pat. No. 2,789,954. The concentrated peroxomonosulphuric acid solution obtained from concentrated sulphuric acid and aqueous hydrogen peroxide is a hazardous chemical and poses a work hazard for operating personnel with a low qualification in handling hazardous chemicals. In many applications, such as in mining and water purification, peroxomonosulphuric acid is not used in concentrated form, but as a dilute aqueous solution.
U.S. Pat. No. 2,789,954 describes a method of making concentrated peroxomonosulphuric acid by flowing together a stream of concentrated sulphuric acid and a stream of hydrogen peroxide at the mouth of a water-cooled condenser, so that the resulting mixture is cooled within several seconds. The cooled mixture is then diluted to 6% by weight peroxomonosulphuric acid by mixing with a stream of water and passing the resulting mixture through a second condenser. The device used in U.S. Pat. No. 2,789,954 is useful only on a laboratory scale, but cannot be scaled up safely to an industrial scale.
WO 92/07791 describes a method of making peroxomonosulphuric acid in an adiabatic reactor, where hydrogen peroxide is injected into a stream of sulphuric acid, flowing through an annular reaction chamber, through an inlet directing the hydrogen peroxide transversely to the sulphuric acid flow. The document proposes to allow the hot concentrated peroxomonosulphuric acid to flow directly into a tank or vessel in which its use is desired or in the alternative to flow it through a pipe immersed in a treatment tank in order to cool it.
However, there still remains a need for a device and a method that provides a dilute aqueous solution of peroxomonosulphuric acid without a risk of exposing operating personnel to a concentrated peroxomonosulphuric acid solution. The instant inventors have developed a device and a method that meets this need.